§1357
Sacraments › … › V. The Sacramental Sacrifice Thanksgiving, Memorial, Presence
We carry out this command of the Lord by celebrating the memorial of his sacrifice. In so doing, we offer to the Father what he has himself given us: the gifts of his creation, bread and wine which, by the power of the Holy Spirit and by the words of Christ, have become the body and blood of Christ. Christ is thus really and mysteriously made present.
Source: Catechism of the Catholic Church (Vatican.va)